266 



PHYSIOLOGICAL REGULATIONS 



later ages water consumption becomes progressively more nearly- 

 proportional to B^^^, as food consumption does (Bruggemann, '38). 

 Or, according to an allometric equation of relative growth R = aB", 

 b decreases progressively with age to a stable value of 0.67. 



The data for bovine represent an early stage in the development 

 of the individual. Those for rat are distinctly late in the life his- 

 tory. The data for bovine caution against basing a broad and 

 attractive generalization upon the data for rat. 



The individuals measured differ not only in body weight, but in 

 age and all that goes with it. Only arbitrarily is weight used above 

 as abscissae, instead of age or total food intake or total bulk of 

 alimentary flora and fauna. 



Fig. 135. Course of total water load (% of Bo), in a young dog Ha at the diverse 

 ages indicated. About 5% of Bq is given by stomach tube on each of 5 days. At agea 

 less than 21 days, each point is the body weight just after urine is drawn by bladder 

 puncture; thereafter the bladder is emptied spontaneously. Eapid excretion of the 

 load is acquired between the 8th and 21st day. Also the specific gravity of the urine 

 becomes less, and becomes so earlier, after the 8th day. New data. 



In dogs a marked change with age in the recovery from water 

 excess can be traced. Water diuresis is not perfected at birth; 

 instead, urinary water output is little faster under positive water 

 load than in water balance. What slow diuresis can be found lasts 

 many hours after water is administered. This fact allows the 

 study of what a dog is like without much equilibration of water 

 content. Rapid water diuresis appears 5 to 21 days after birth 

 (fig. 135), at which time the adult response is fully developed. 

 While the time of acquirement of water diuresis differs slightly 

 among litters of pups, and even in the individuals of one litter (fig. 

 136), there is no doubt of its finality. Body size or state of nutri- 



